Category Archives: Technical

It’s time for the two parts of my retrocomputing life to collide in the most resourceful of ways…

My “europlus Refurbapalooza”, whereby I’m trying to get all my europluses operational, has been the thrust of my two Retrochallenge entries in 2016/10 and 2017/04. With the vagaries of “real life” impinging more the second time around (just that time of year, I think), I’ve gotten even less done this month…but that doesn’t mean I’ve been entirely unproductive.

I’ve been able to test the electrolytic capacitors in all seven of my europlus Astec AA11040C power supply units (PSUs). Despite 14 electrolytic capacitors per PSU (so 98 total) and the PSUs being at least 35 years old, I was pleased to find only four capacitors are exceeding (or almost exceeding) their maximum ESR (Electrical Series Resistance) value.

I’m also going to follow the general guideline to replace the C1 filter capacitor, even if the original hasn’t blown (two of the seven originals have definitely blown, and a further three or four are showing cracking in their plastic covering). I’ve bought all the replacement capacitors I need, and hope to install them all and test the PSUs during WOzFest PR#6.

While carrying out these ESR tests, I wanted a ready-reference to the capacitor specifications for determining the correct ESR value to be testing and for when I came to purchase replacement capacitors.

As a non-expert, I also wanted a reference to the position and polarity of the solder points for each capacitor on the underside of the PSU circuit board – I was testing the capacitors “in-circuit” rather than removing them for testing (while not ideal, I’m trying to keep the task manageable).

I had found online a scan of a 1982 document from Apple which provided a great start to what I wanted. It has schematics and circuit board layouts for several Apple PSUs, as well as a components list for each of the PSU models it includes.

Although it has info on the AA11040B (while I have AA11040Cs), upon inspection I believe the primary difference is the AA11040C is the 230V version of the AA11040B with the “115V Select” wire removed and a 250V/2A fuse replacing the 125V/2.75A fuse.

So I decided to prepare just the sort of ready-reference I would have liked to have started with. Over several iterations to refine the design and info included, and taking input from enthusiasts with more PSU repair experience than me, (thanks Mark, Martin, Jon, Geoff and John!), I’ve created the “WOzFest Labs Apple Astec Power Supply Unit AA11040B/C Electrolytic Capacitor ‘Spec & Check’ Sheet” (it just rolls of the tongue!) – and I’m pleased to announce the release of v1.0 of this “Spec & Check” sheet for use by other enthusiasts looking to test and refurbish their AA11040B/C PSUs.

This release is the major result of my Retrochallenge 2017/04 entry and in line with WOzFest PR#6’s theme of “Preservation”.

I’ve designed the sheet so that it can be printed at 100% on A4 (297✕210mm) or US Letter (8.5″✕11″) without any information being cropped. When printed at 100%, the picture of the underside of the PSU circuit board is “life size”, so it’s easy to correlate the highlighted solder points to a physical circuit board.

The sheet can be used as a checklist of capacitors that are in or out of spec, has the maximum ESR values listed for each capacitor (as well as other specs) in both tabular and “call out” forms, and the polarity of the solder points are annotated and colour-coded.

This is only v1.0, and suggestions/corrections from other enthusiasts will be included in updates. If I’m able, I’ll also release versions for other PSU models that Apple used in Apple ][s.

This is the first resource issued under the name “WOzFest Labs”, and hopefully there’ll be many more (I’ll probably re-release my Silentype Font under that name, too). I’d be interested in collaborating on other resources, too, so hit me up if you have any ideas you”d like to work on with me.

A few notes:

I’ve provided specs and solder points for the C1 filter cap to ease replacement of this component along with any out-of-spec electrolytic capacitors;

Capacitors C13 and C14 are in parallel on the circuit, so testing either one to half the usual maximum ESR is adequate when testing them “in-circuit” – if capacitors are removed for testing, double the stated maximum ESR value for these two capacitors;

Capacitors rated to 105°C are recommended;

The 1982 document from Apple has at least two errors in the components list for the AA11040B PSU, so check its information carefully if you’re using it as a reference.

If you’re wondering about the typewriter-like font I used, it’s Prestige Elite, which, by my reckoning, is the font used in early Apple spiral-bound manuals such as The Applesoft Tutorial. It’s my theory that these early manuals were “typeset” using material printed by the ubiquitous IBM Selectric typewriter.

So, other than some soldering, testing and writing a recap on my re-capping adventures, that’s pretty well it for my Retrochallenge entry this time around. I’m looking forward to getting to the meat of my europlus refurbishment – testing (and hopefully repairing) motherboards – next go ’round in October!

So, in preparation for WOzFest $04, I decided to give my five Disk ][s a bit of TLC and try and get them all working (Figure 1).

Step one is to crack them open with a view to cleaning the read/write heads and possibly lubricating the rails. Luckily, they’re pretty simple devices to get into – four screws on the underside (Figure 2) and the upper case slides off the drive mechanism, showing the bare drive mechanism and the analog card that drives it (Figure 3).

To get to the read/write head, another two screws holding the analog card need to be removed and the card can be slid out of two slotted guides towards the rear of the drive (near the “D”s at the rear corners of the analog card). The analog card has two cable connections – for quick and simple work, only the one closest to the front of the drive (with a molex connector) needs to be disconnected to allow the analog card to be flipped upside down over the rear of the drive (Figure 4). This cable’s connector is “keyed” with a missing hole for the missing pin on the header to aid alignment and orientation.

Some Disk ][s have a plate covering the read-write head – this is simply clipped into place and easy to remove (Figure 5). You can then (gently) raise the sprung component (not too high!) of the drive head (which holds the disk against the read/write head) to clean the actual read/write head itself (Figure 6).

I’m leaving the outer covers off and the analog card unsecured in the drives I’m going to be using for disk imaging – this allows easy access to the drive head for cleaning. It’s amazing how quickly gunk builds up on the read/write head. I’m using isopropyl alcohol and cotton tips to clean the heads.

I had to lubricate the rails the head mechanism travels along in one drive – I used white lithium lubricant applied liberally with a cotton tip, then wiped off the visible excess with a paper towel after moving the head mechanism up and down the rails a few times.

Unfortunately, while working on my drives, I connected one to the interface card in the Apple ][ incorrectly – while I had it properly aligned along the length of the connector, I only plugged it into the outer row of pins, rather than to both rows (Figure 7). Snap, crackle, pop! I’d burnt out something on the drive’s analog card.

I was pretty sure the next drive I connected to the Disk ][ interface card I was using was connected correctly, but it also popped and was no longer working. I wondered if maybe something on the interface card had blown as well?

Visually, I could tell that the 74LS125 logic chips on the Disk ][ analog cards had blown (Figure 3 and Figure 8). By this point I had some confirmed working drives, so I swapped in a 74LS125 from a working drive’s analog card – the drives still didn’t work (I was using a different interface card in case the one I’d been using was also now a dud).

At this point I swapped a known good analog card into both drives in turn just to make sure that’s where the problem was and both drives worked, so I went back to swapping other chips from a known good analog card. Luckily, there aren’t many chips and I quickly determined both analog cards’ MC3470 chips were also faulty, even though there was no visible damage.

I was able to buy 74LS125s from my local Jaycar electronics store (for AU$1.75 each), and I bought replacement MC3470s from eBay (for about AU$2.50 each including delivery) – I bought enough of both chips to test a repaired drive with the suspect interface card. If the drive blew again I would be able to replace those two chips again.

As it turns out, that interface card didn’t blow up a repaired analog card, so I think it’s OK and I must have connected the second drive incorrectly as well. I vow: never again!

So, after all that, I now have five operational Disk ][s, and a bit more experience and confidence in doing my own retro repairs (which bodes well for my Retrochallenge entry).

Feel free to share your own Disk ][ damage and repair stories in the Comments section.